Gasket, method of manufacturing and apparatus for manufacturing same

ABSTRACT

A gasket ( 1 ) has a gasket core ( 2 ) and an outer gasket layer ( 4 ) covering the gasket core ( 2 ). At least one of the two sealing materials that make up the gasket has two reactive components before they are extruded, with said components chemically reatcting with one another as they are combined and/or extruded. The extruded core may be formed of a two-component resin which is at least one of an elastomer and a foam. The flexible outer layer may be a synthetic resin which is at least one of an elastomer and a foam. The outer layer may be electrically conductive, ultra-violet resistant, or resistant to the environment in which the gasket is to operate. Also taught are methods of apparatus for the manufacture of such gaskets

FIELD OF THE INVENTION

This invention relates to gaskets, their manufacture and apparatus formanufacturing same.

BACKGROUND OF INVENTION

There are many applications in which outer surface layers of a gasketand an inner core of the gasket require different and possibly mutuallyinconsistent properties, and thus proposals have been made for gasketsformed with an outer layer and an inner core of different materials.

For example, the prior art describes the production of prefabricatedgaskets for electromagnetic shielding consisting of an inner core and anouter layer. The inner core provides the gasket with physical propertiessuch as compression deflection, tensile strength and elongation. Theouter layer provides the surface with properties such as electricalconductivity. Both the inner core and the outer layer are elastomeric.The two layers can be co-dispensed (U.S. Pat. No. 4,968,854) or theinner core can be formed first with the outer layer applied afterwards(U.S. Pat. No. 5,141,770). The inner core usually consists of aone-component thermoplastic resin or a one-component, heat-curedextruded rubber. The outer layer is also a one-component thermoplasticresin or a one-component, heat-cured extruded rubber. The outercomponent can also be made from a low-viscosity coating dispersioncontaining an elastomeric binder, a metallic material, a curing agentand a diluent, such as an organic solvent. The solvent is used tosubstantially reduce the viscosity of the coating, the inner core beingin this case extruded and solidified prior to the application of thecoating.

Gaskets may be used for electromagnetic shielding of electronic casings,and in the course of increasing miniaturization of casings, are placedin a free-flowing state from a nozzle directly onto a casing section tobe sealed, where they harden. For the electromagnetic shielding ofcasings, the outer gasket layer usually consists of a sealing materialthat is a good conductor of electricity, while the inner layer, or aninner gasket core, is usually made of a sealing material that is a poorconductor of electricity or does not conduct electricity at all. Such aseal combines the good electrical properties of the outer layer with thegood mechanical properties of the inner core, with the outer layernormally exhibiting worse mechanical properties, i.e., as regardscompressibility, due to the addition of metal articles.

Such a gasket is known, for example, from the unexamined Europeanapplication EP 0 895 49 A2. This publication describes an electricallyconductive seal that is produced through coextrusion of a siliconpolymer and a silicon polymer with silver components to form a sealingmaterial cord and a conductive medium cord enclosed by the sealingmaterial cord. The outer, electrically conductive cord through thesilver components serves to connect electrically conductive casinghalves, in whose opening the seal is designed, in order to shieldelectromagnetic radiation from the casing interior or into the casinginterior.

The use of a silicon polymer involves some disadvantages. Silicon is notvery compressible, thus, when reducing the size of the casing to beshielded with the consequent corresponding reduction in size of thegasket diameter, good compressibility of the sealing material isrequired in order to compensate for unevenness on the surfaces of thecasing and to ensure that the gasket rests against all the surfaces tobe sealed. Furthermore, silicon, which is applied in a viscous state,dries when exposed to air, and continues to harden in the process, isrelatively difficult to process and comparatively expensive.

SUMMARY OF THE INVENTION

The present invention provides a gasket which combines sealing materialswith various mechanical, chemical, and/or electrical properties that canbe produced in a simple manner, and which preferably have goodcompressibility.

In an embodiment, at least one of the sealing materials has, before itis dispensed, at least two reactive components that react chemicallywith one another after they are combined and/or the components aredispensed. Polyurethane may be used as a sealing material, consisting oftwo components that react with one another after they are combined orafter being dispensed into the air, and form a sealing foam. The resultof the chemical reaction after the curing is a foam gasket that has goodcompressibility. The two components forming the polyurethane can beeasily processed. Thus, these two components, which are suitable for themanufacture of the inner gasket core as well as the outer gasket layer,can be dispensed or processed in liquid state—and therefore a state thatlends itself well to processing—onto the surface to be sealed, whileforming a cord, where the two components react with one another andcure. Moreover, polyurethane is reasonably priced.

An advantage of a sealing material that has at least two initialcomponents to be used for at least one of the sealing layers is that thegasket assumes its desired characteristics and cures only after it isput in place through the reaction of at least two components, while thecomponents that have already been mixed but have not yet reacted withone another can be easily worked with and can be dispensed or processedby means of a nozzle. The length of time that the components remainworkable without reacting with one another depends on the material. Inan embodiment, one can use initial components that react with each otheronly after they are dispensed into a reaction-promoting atmosphere in amixed state.

The invention thus provides a versatile co-dispensed gasket and a methodfor its manufacture, based on the use of a two-component core materialsetting to an elastomer or foam, to which is applied an outer layerwhich may be a further two-component material, setting to an elastomeror foam, or a solvent-based coating, either co-dispensed with the corematerial or applied to the latter subsequently. In this context,“two-component” as applied to the core material, should be construedbroadly. The core material must be able to cure or set to a stable finalmaterial within the outer layer. This can be achieved with materials nottraditionally considered to be two-component materials, as describedfurther below. The core material should have a consistency such that itcan be dispensed but will remain in situ after dispensing and duringcuring.

This enables the core and/or the outer layer to be foams as well aselastomers. With a suitable choice of two component compositions orsolvent-based coatings, the entire process can be carried out at ambienttemperatures. The co-dispensing process can be used to provide form (andfoam) in place gaskets, which is not practicable with any known processfor two-component gaskets of the types concerned. Rather than formingthe gasket in situ, it may be co-dispensed into a mould and then curedto provide a desired profile. If low density co-dispensed foams areused, the process is highly cost-effective, while the ability to usefoams and/or elastomers with widely different properties makes it veryversatile. The use of a mould also means that relatively low viscositymaterials may be used, whereas in situ formation usually requires thematerials to be highly viscous or thixotropic in order that they mayremain in situ while curing or setting. The core and outer layers may beformed of different density foams, or the outer layer may be of amaterial selected to provide a thin, tough flexible skin.

Accordingly, the invention provides a gasket comprising a core formed bya two-component resin which, when set, is at least one of an elastomerand a foam, over which is applied a flexible outer layer of a syntheticresin which, when set, is at least one of an elastomer and a foam.

The invention also includes a method for the manufacture of a gasketaccording to the invention and an apparatus for the manufacture of agasket according to the invention.

The apparatus includes two coaxial nozzles, an inner nozzle for thematerial of the gasket core and an outer nozzle enclosing this innernozzle for the material of the outer gasket layer. In an embodiment,these nozzles or at least one of these nozzles can be usedinterchangeably in the nozzle head, as a result of which the diameterand/or the sheathing thickness of the gasket can be varied in a simplemanner.

Further features of the invention will be apparent from the followingdescription and examples of embodiments of the invention.

SHORT DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section of a gasket according to the invention, thegasket placed on a section of casing;

FIG. 2 is a cross-section of a gasket according to the invention, withthe gasket compressed in a closed casing;

FIG. 3 is a cross-section of a gasket formed in a groove of a casing;

FIG. 4 is a section of an apparatus for the manufacture of a gasketaccording to the invention;

FIG. 5 is an enlarged section from FIG. 4;

FIG. 6 is a schematic diagram of an apparatus for producing gaskets ofthe invention;

FIG. 7 is a fragmentary cross-sectional view of two machine parts, onewith a groove to be gasketed with a foam-in-place co-dispensed gasket;

FIG. 8 is a cross-sectional view of a mould used to form prefabricatedgaskets of the invention;

FIG. 9 is a fragmentary cross-sectional view showing an overlap of endsof an extrusion forming a co-dispensed gasket.

FIG. 10A to 10D are end views of some different nozzle arrangements thatcan be utilized in performing the method of the invention.

DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a cross-section of a gasket 1 according to the invention,with the gasket placed on a surface 5 of a casing part 6A. The gaskethas an inner gasket core 2 and an outer gasket layer 4 that completelyencloses the inner gasket core 2 in the embodiment shown. To manufacturethe gasket 1, the first, free-flowing sealing material for the gasketcore 2, and the second free-flowing sealing material for the outergasket layer 4, are placed on surface 5 where the sealing materials cancure.

At least one of the two sealing materials has, before being dispensed,at least two components that chemically react with one another afterthey are combined and/or dispensed into a reaction-promoting atmosphere.Air is a particular example of a reaction-promoting atmosphere, whilepolyurethane is an example of a sealing material that has at least twocomponents. The components of polyurethane cure after the reaction,while forming a foam that has good compressibility and therefore adjustswell to the contours of the casing to be sealed.

The outer gasket layer 4, which can also consist of a sealing materialthat has at least two initial components, may be electrically conductiveso that it can connect conductively two conductive halves of the casing,6A, 6B in a closed casing as shown in FIG. 2, and consequently so thatit can electromagnetically shield the electronic components found in thecasing. The material of the outer gasket layer 4 can also be chosen insuch a way that it is UV- and/or acid-resistant or has this property inaddition to the electric conductivity. The gasket 1 is compressible sothat it can fit closed casing 6A, 6B all over the casing halves 6A, 6Band level out unevenness on the sealing surfaces of the casing halves6A, 6B.

The outer gasket layer 4 may consist of a material that has a closedsurface. Sealing foams, such as polyurethane, have pores that liquid canpenetrate, and thus may allow the liquid to penetrate the casing to besealed. In a gasket core 2 having pores, the outer gasket layer 4therefore may comprise a sealing material that has no pores, forexample, silicon. For the outer gasket layer, a sealing material thathas at least two initial components that react with one another afterthey are combined and/or are dispensed while forming an outer gasketlayer 4 with a closed surface is also taught.

FIG. 3 shows a gasket 1 of the invention, which is formed in a groove 9of a casing part 7. The groove 9 supports the positioning of the gasketcore that is dispensed, with the core being still soft. The disadvantagein placing the sealing materials in a groove 9 is that there can beinsufficient ventilation for drying the sealing in the groove 9. As aresult, in some sealing materials used for the outer gasket layer 4, nointegral skin impermeable to liquid forms on the surface of the outergasket layer 4 in the area of the groove 9. The risk is that moisturegets through the seal in the area of the groove 9, and in this manner,the moisture penetrates the interior of the casing. To avoid thesedisadvantages, the outer gasket layer 4 may consist of material whichforms an integral skin on the surface even when ventilation is badduring the curing. Such a sealing material can have at least two initialcomponents that react with each other after they are combined or afterthey are dispensed.

The thickness of the outer gasket layer 4 may be less than the diameterof the gasket core 2. In a seal for electromagnetic shielding of acasing, in which only the outer gasket layer 4 needs to be electricallyconductive, one can save on resources such as silver as conductivematerial.

Of course, the inner gasket core 2 as well as the outer gasket layer 4can consist of a sealing material that has at least two components thatchemically react with one another and cure after they are combinedand/or dispensed into a reaction-promoting atmosphere. In the process,electrically conductive particles can be added to the components for theouter layer 4.

The final properties of the gasket 1 will be exhibited only after thereaction of the initial components of the respective gasket layers 2, 4,i.e., the sealing material arises only as a result of the initialcomponents reacting with one another after they are combined and/ordispensed. Depending on the application, there are desired properties ofthe sealing material that can be influenced by the selection of theinitial components, such as the foaming of the components during thechemical reaction, the formation of a sealing layer with a closedsurface, or the curing while an integral skin is formed even whenventilation is not good. Preferred as initial components are liquidcomponents that are easy to work with and can be easily dispensed ontothe surface to be sealed before the chemical reaction occurs. Dependingon the choice of the initial components, the chemical reaction may takea certain duration after the initial components are combined, and/or itmay occur only after the initial components are dispensed into areaction-promoting atmosphere. The start time of the reaction, or thetime period after the time the components to react after they arecombined, can be adjusted by selecting the components in such a way thatsufficient time remains for dosing the gasket core onto the sealingsurface after the initial components react with one another.

One embodiment of the invention provides for the sealing layer tocompletely enclose the gasket core and to have electrically conductiveparticles. This embodiment ensures that two conducting halves of thecasing are always connected in an electrically conductive manner throughthe seal, independent of which part of the surface of the seal thecasing halves lie against.

A further embodiment provides that the outer gasket layer consists of amaterial that has a closed surface after the curing.

Silicon is an example of such a material. Sealing materials that havetwo initial components that chemically react with each other after theyare combined and/or dispensed into a reaction-promoting atmosphere inorder to form a gasket with a closed surface can also be used. The useof such material prevents moisture from penetrating the pores of theseal, and consequently, the interior of the casing.

Furthermore, it is possible to use for the outer gasket layer a materialthat exhibits a better resistance against various environmentalinfluences, e.g., the outer gasket layer may have a material resistantto UV-light or acid, in order to adapt the seal to the respectiveconditions for use.

Sealing materials may be extruded in a viscous state into the grooves ofthe casings in which they cure in order to form the seal. However, somematerials may cure in the groove, particularly in the groove base, wherethere is poor ventilation, without forming a so-called integral skin onthe scaling surface. The risk is that moisture will penetrate thegasket, and from there, the interior of the casing. The material formingthe outer gasket layer is therefore preferably a sealing material thatcures even in the grooves, i.e., even when ventilation is not good,while forming an integral skin on the surface. A sealing material thathas at least two initial components comes into consideration as sealingmaterial, in which the two components, after being combined or afterbeing dispensed onto the surface to be sealed react with one another andcure, even when ventilation is not good, while forming an integral skin.

FIG. 7 is a cross-sectional view of a part 128 with a groove 126 to begasketed, illustrating one way in which a co-dispensed gasket can beformed-in-place. The cover 130 can be applied after the gasket isformed. The surface of the groove and the composition used for the outerlayer will determine whether the outer layer bonds to the surface. Theco-dispensed gasket can also be applied on a flat surface rather than ina groove.

FIG. 8 is a cross-sectional view of a mould used to shape prefabricatedgaskets in accordance with the invention. The gasket is dispensed intothe bottom of the mould 132. The cover 134 is applied before the gasketsets. In this case, the outer layer and the mould surface are selectedso that the cured gasket will release from the mould surface.

FIG. 9 is a longitudinal cross-sectional view of a portion of aco-dispensed gasket in which the beginning and end of the extrusionoverlap. This type of overlap is created by starting the dispensing ofthe outer layer material 136 before starting dispensing of the corematerial 138, and continuing dispensing of the outer layer materialafter dispensing of the core material has been stopped. This may beconveniently achieved by using valves 111 and 113 in FIG. 6. Acontinuous, closed-loop gasket is formed if the ends 140 and 142 of thedispensed material are overlapped. An open-ended gasket is formedwithout the overlap. Gaskets of many sizes and shapes can be made bymounting the nozzle 118 of FIG. 6 on a programmable robot.

FIGS. 10A to 10D are end views of some different nozzle configurationsfor co-dispensing gaskets in accordance with this invention. It will benoted that the nozzles are not necessarily concentric or of a similarprofile, and that the nozzle for the outer layer material may not fullysurround that for the core material, providing a gasket in which thecore material is not fully enveloped by the outer layer. This may benecessary or desirable in some applications.

As shown in FIGS. 10A and 10B, the relative thickness of the outer layerrelative to the core layer may vary. It will normally be desirable thatthe outer layer and core are bonded securely together, and this will befacilitated if both the core and the outer layer are formed by resins ofthe same general type, e.g., polyurethane.

An apparatus whose nozzle head is shown in FIG. 4, and an enlargedpartial section of which is in FIG. 5, can be used to manufacture agasket according to the invention.

The nozzle head 10 has a first, continuous borehole 11 leading to asecond borehole 12 inclined at an angle against the axis of the firstborehole 11. An inner nozzle 13 is inserted into the first borehole 11,the nozzle having a diameter less than the inner diameter of the firstborehole 11, so that a ring-shaped passage gap remains free between theexterior circumference of the inner nozzle 13 and interior circumferenceof the first borehole 11. The inner nozzle 13 is pressed into a firstinsert 14, which is inserted into the enlarged influx-side and (shown inthe upper portion in the figure) of the first borehole 11. The firstinsert 14 can be inserted in the seat in the nozzle head 10 or can bescrewed into it in a detachable manner so that the inner nozzle 13fitted into the first insert 14 can be interchangeable. On theinflux-side end of the first insert 14 and the inner nozzle 13 isinserted a first shutoff valve 15. A feed for the material to the innergasket core 2 is connected to an influx-side receptacle 16 of the firstshutoff nozzle 15. This feed can be formed in a known manner. If thematerial is a two-component material, the feed consists of atwo-component mixing apparatus, in which the two components are mixedand fed through the shutoff valve 15 and the inner nozzle 13.

A second shutoff device, e.g., in the form of a second shutoff valve 17,which can likewise be screwed into the nozzle head 10, is fastened tothe influx-side end of the second borehole 12. The second shutoff valve17 also exhibits a receptacle 16, to which a feed is connected, throughwhich the material of the outer feed is connected, through which thematerial of the outer gasket layer 4 is fed. Here as well, the feed canbe a one-component dosing device or a two-component-mixture and dosingdevice, as already known in the art. The first borehole 11 is enlargedin its outlet end, shown in the lower portion of the figure. In thisenlarged end, a second insert 18 can be inserted, into which an outernozzle 19 is fit in. The second insert 18 exhibits a continuous boreholeinto which the outer nozzle 19 has been inserted. The inner diameter ofthe outer nozzle 19 or the borehole of the second insert is larger thanthe outer diameter of the inner nozzle 13, as a result of which the ringslot between the first borehole 11 and the inner nozzle 13 in the secondinsert 18 and the outer nozzle 19 continues. The second insert 18 may beinserted by means of an outside screw into an inner screw of theend-side enlargement of the first borehole 11 so that the second insert18 can be interchanged with the outer nozzle 19.

For the manufacture of a gasket according to the invention, the firstsealing material or initial components of the first sealing material areput in through the first shutoff valve 15 and the second sealingmaterial, or initial components of the second sealing material, throughthe second shutoff valve 17 of the nozzle head. At least one of the twosealing materials consists of at least two free-flowing components thatchemically react with each other after they are combined and/ordispensed into a reaction-promoting atmosphere. The chemical reactionmay be, for instance, a sealing foam that has good compressibilityarising from the free-flowing components, a sealing material with closedsurface, or a sealing material that also ventilates even whenventilation is not good, while forming an integral skin. Electricallyconductive particles may be added in the process to the second sealingmaterial or the components.

To extrude the sealing materials, the first sealing material is putunder pressure by the first shutoff valve 15 and the inner nozzle 13.Accordingly, the second scaling material, under pressure from the secondshutoff valve 17 and the second borehole 12, is pressed into the firstborehole 11 and the outer nozzle 19, which enclose the inner nozzle.

The first and second sealing materials are separated from one another inthe nozzles 13, 19. They meet each other only at the common outlet endof the inner and outer nozzles 13, 19, where gasket core 2 is formed bythe first sealing material. The core comes out of the inner nozzle 13completely enclosed by an outer gasket layer 4 out of the second sealingmaterial, formed by the outer nozzle 19 and the outer surface of theinner nozzle 13. The sealing materials are chosen such that they do notmix, or mix very little when they meet, but that they neverthelessadhere well to each other.

The nozzle head 10 is fed through the casing part to be sealed so that aviscous gasket core merging from the nozzles is placed directly onto thecasing part, and adheres and cures there in order to form the gasket.The sealing strand may be dispensed onto the casing under an atmospherethat promotes the chemical reaction of at least two components, whichcomprise at least one of the two sealing materials.

Through the shutoff valves 15 and 17, it is possible to block the feedof the components into the nozzle head 10 at the end of the dosingprocedure so that no more component material enters the nozzles andboreholes of the nozzle head 10, preventing a drip of the sealingmaterial at the end of the dosing procedure.

With the apparatus according to FIG. 4, a gasket for an electromagneticshielding can be produced completely out of polyurethane, in which onlythe outer gasket layer is electrically conductive. For this, the twoinitial components of polyurethane are fed to the first hollow space andthe two initial components made of polyurethane and an electricallyconductive material are fed to the second hollow space. After the twosealing materials are dispensed, the components of the polyurethanereact, forming a sealing foam in which the outer gasket layer iselectrically conductive.

The diameter of the inner gasket core 2 is largely determined by thediameter of the inner nozzle 13 and the thickness of the outer gasketlayer 4 is largely determined by the difference between the outerdiameter of the inner nozzle 13 and the inner diameter of the outernozzle 19. By means of the first insert 14, the inner nozzle 13 can bechanged in order to vary the diameter of the inner gasket core 2. Bymeans of the second insert 18, the outer nozzle 19 can be changed inorder to vary the outer diameter of the outer gasket layer 4, andconsequently, the entire gasket. The thickness of the outer gasket layer4 can likewise be varied by exchanging the nozzles 13 and 19.

FIG. 6 is a schematic of a dispensing apparatus for producing gasketsusing a two-component resin system for the inner core and atwo-component resin system for the outer layer. It comprises reservoirs102, 104, 106 and 108. Reservoirs 102 and 104 hold the two components ofthe inner core material. Reservoirs 106 and 108 hold the two componentsof the outer layer material. Metering pumps 102A, 104A, 106A, and 108Adispense correct quantities of each component. The components of theinner core and outer layer are passed through mixers 110 and 112 andshut-off valves 111 and 113 via tubes 142, and are then dispensedthrough co-axial tubes 114 and 116 of nozzle 118 to form a co-dispensedgasket 120, having a core 127 and an outer layer 124. The resultinggasket will have an elastomeric or foam inner core 127 and anelastomeric or foam outer layer 124.

Although the following examples make use of conventional two-componentthermosetting resin systems, the term two-component in the context ofthe invention should be taken to include systems in which the secondcomponent is a gas or simply moisture. A number of moisture-curingfoamable compositions are known, and these may be used for the corematerial, as well as for the outer layer, provided that the moisturerequired for curing may reach the core. Thus the necessary moisture maybe contained in the outer layer material or be produced as a by-productof its curing or may permeate through the outer layer, if the latter isan open cell foam, or the inner core may be moisture-cured by directapplication of moisture, if the core is extruded using a nozzle whichprovides an extrusion in which the core is not fully enveloped by theouter layer. As a further alternative, a second component in the form ofa pressurised gas such as nitrogen may be added in the dispensing systemto a molten thermoplastic first component. On emerging from theextrusion nozzle, the nitrogen expands to foam the first component whichrapidly sets to form a foam. The following examples however make use ofconventional two-component core materials.

EXAMPLE 1

A gasket of approximately a half-round cross-section, 8 mm in diameter,and having an outer layer 0.5 mm thick was formed by co-dispensing oftwo-component polyurethane foams as follows. An inner core was atwo-component, thixotropic material available from Chemque Inc.,Indianapolis, Ind., under the designation CHEM-CAST 624™, the mixingratio of components A & B of that material being 100 parts to 18.5 partby weight. It cures to a flexible, polyurethane foam with the followingproperties when cured: Shore OO Hardness:  45 Compression Deflection:3.0 psi Foam Density: 0.3 gm/cm³

The outer layer was an electrically-conductive thixotropic materialavailable from Chemque Inc. under the designation CHEM-CAST 906™, themixing ratio of components A & B of that material being 100 to 3.1 partsby weight. The material cures to a flexible polyurethane foam with thefollowing properties: Shore A Hardness:   10 Compression Deflection:12.0 psi Foam Density:  0.6 gm/cm³ DC Volume Resistivity: 0.10 ohm · cm

The inner core constituted approximately 76% of the total volume. Theouter layer constituted approximately 24% of the total volume. The innercore contributed to forming a very soft gasket with good compressionrecovery, low density and low cost. The outer layer contributed toproviding a high electrical conductivity of the finished gasket. Theeffects of high cost, high hardness and poor compression recovery of theouter layer are minimized by co-dispensing. The overall result was asoft flexible resilient gasket with good conductivity at reasonablecost.

EXAMPLE 2

A gasket was formed of similar dimensions to that of FIG. 6, except thatthe outer layer had a thickness of 0.25 mm. In this case, the inner corewas formed from CHEM-CAST 624™ mixed as described in Example I toprovide a flexible, MDI-based polyurethane foam. This foam has poor UVresistance and outdoor weathering properties:

The outer layer was a white-pigmented, two-component low-viscositymaterial, available as CHEM-DEC ER96071™ from Chemque Inc., with parts A& B mixed in the ratio of 100 to 110 parts by weight. This cures to aflexible polyurethane elastomer incorporating an aliphatic isocyanatefor good UV resistance, and having a Shore A hardness of 50.

The two layers of this gasket were co-dispensed at the same time. Theinner core provides a very soft gasket with good compression recovery,low density and low cost, while the outer layer provides good UV andweather resistance and toughness to the gasket.

EXAMPLE 3

A gasket was formed by co-dispensing, having similar dimensions to thoseof Example 2. The core layer was a two-component thixotropic materialavailable from Chemque Inc. under the designation CHEM-CAST 628-231™,with components A & B mixed in the ratio of 87 to 100 by weight. Itcures to a flexible, silicone foam with the following properties: ShoreA Hardness:   15 Compression Deflection:  4.0 psi Foam Density: 0.45gm/cm³

The outer layer was a two-component, electrically conductive,thixotropic material available from Chemque Inc. under the designationCHEM-CAST ER 96088-3™ with components A & B mixed in the ratio 100 to4.6 by weight. It cures to an electrically-conductive flexible siliconeelastomer. It was found that the addition of solvent reduced viscosityfor ease of application. As an alternative to co-dispensing, the outerlayer may be applied after curing of the inner core layer. Shore AHardness:   70 Elastomer Density:  2.9 gm/cm³ DC Volume Resistivity:0.15 ohm · cm

The elastomer of the outer skin adds electrical conductivity andtoughness to the soft resilient inner foam core.

1-44. (canceled)
 45. An apparatus for the manufacture of a sealcomprising: a nozzle head having a feeding side and an outgoing side; aninner nozzle arranged within the nozzle head for feeding a first sealingmaterial; an outer nozzle arranged within the nozzle head for feeding asecond sealing material, wherein the outer nozzle at least partially,coaxially encloses the inner nozzle.
 46. The apparatus according toclaim 45 wherein the nozzle head further comprises a first borehole,wherein the inner nozzle is coaxially inserted into the first borehole,wherein the inner diameter of the first borehole is larger than theouter diameter of the inner nozzle, and the outer nozzle is insertedinto the first borehole.
 47. The apparatus according to claim 46 furthercomprising a second borehole connected to the side of the firstborehole.
 48. The apparatus according to claim 45 further comprising adetachable first insert connected to the inner nozzle, wherein the innernozzle and the detachable first insert can be detachably inserted fromthe feeding side of the nozzle head into the first borehole.
 49. Anapparatus according to claim 48 wherein the inner nozzle isinterchangeable.
 50. An apparatus according to claim 45 furthercomprising a detachable second insert connected to the outer nozzle,wherein the outer nozzle and the detachable second insert can bedetachably inserted from the outgoing side of the nozzle head into thefirst borehole.
 51. An apparatus according to claim 50 wherein the outernozzle is interchangeable.
 52. An apparatus according to claim 45further comprising a first feeding passage connected to the inner nozzleto supply the first sealing material to the inner nozzle and a secondfeeding passage connected to the outer nozzle to supply the secondsealing material to the outer nozzle.
 53. An apparatus according toclaim 52 further comprising a shutoff device inserted into the firstfeeding passage, into the second feeding passage, or both.
 54. Anapparatus according to claim 52 further comprising two reservoirsconnected to the first feeding passage, wherein the two reservoirs holdcomponents of the first sealing material.
 55. An apparatus according toclaim 52 further comprising two other reservoirs connected to the secondfeeding passage, wherein the two other reservoirs hold components of thesecond sealing material.
 56. An apparatus according to claim 54 furthercomprising a first mixer connected between the first passage and the tworeservoirs, wherein the components of the first material are mixed inthe first mixer.
 57. An apparatus according to claim 55 furthercomprising a second mixer connected between the second passage and thetwo other reservoirs, wherein the components of the second material aremixed in the second mixer.